Mller glial cells (MGs) are the primary support cells in the vertebrate retina. In cold-blooded vertebrates such as zebrafish, MGs are a source of stem cells for they can readily re-enter the cell cycle and replenish lost neurons, establishing a powerful self-repair mechanism. In mammals, however, MGs are naturally quiescent and lack regenerative capability. Photoreceptors are the most abundant cells in the mammalian retina and they mediate the first step in vision. The death of photoreceptors is a leading cause of vision impairment and blindness in major retinal degenerative diseases including age-related macular degeneration (AMD) and retinitis pigmentosa (RP). Extensive research efforts aimed at restoring the regenerative capability of MGs in mammals have met with little success. Current strategies for MG-derived photoreceptor regeneration rely on retinal injury and treatment of the whole retina with various factors. Retinal injury kills retinal neurons in the first place. Global treatment of the entire retina may lead to undesirable side effects in untargeted cells. The long-term goal of our research is to understand the molecular and cellular pathways underlying MG-derived photoreceptor regeneration, and to develop strategies to activate the regenerative capability of mammalian MGs for retinal self-repair. We propose to reprogram adult mouse MGs, in vivo, for regeneration of rod photoreceptors without retinal injury, through the following Aims: Aim 1) Investigate whether Wnt signaling is an injury-induced signaling pathway to activate MG proliferation. We will examine whether neurotoxic injury activates Wnt signaling and further test whether inhibition of Wnt signaling suppressed injury-induced MG proliferation. To target MGs cell-type-specifically, we will develop a gene transfer method targeting MGs cell-type-specifically. Aim 2) Restore the retinal progenitor/stem cell status of MGs through activation of Wnt signaling, without introduction of retinal injury. We will investigate whether gene transfer of ?-catenin activates Wnt signaling and MG proliferation without retinal injury. GSk3? regulates Wnt signaling by phosphorylation of ?-catenin leading to its degradation. We will examine whether deletion of GSK3? activates Wnt signaling and MG proliferation without retinal injury. Aim 3) Guide the differentiation of MG-derived retinal progenitor/stem cells to rod photoreceptors. We will guide the differentiation of MG-derived retinal progenitor/stem cells by gene transfer of transcription factors that are essential for rod photoreceptor cell fate determination and differentiation during retinal development, and test whether MG-derived new rods develop molecular, structural, and functional properties of native rods. Our proposed research will significantly advance our understanding of the basic mechanisms and functional implications of MG-derived rod photoreceptor regeneration in adult mammalian retina, and will set the stage for retinal self-repair in a major group of retinal degenerative diseases typically characterized by photoreceptor degeneration.